This invention relates generally to human spinal surgery and, in particular, to methods and apparatus for augmenting the annulus fibrosis while controlling vertebral motion, thereby preventing additional annular tears and attendant discomfort.
According to human anatomy, spinal function is dependent upon the intervertebral disc and the facet joints. In a sense, the annulus fibrosis, nucleus pulpous, and the facet joints form the legs of a three-legged stool.
To restore disc height resulting, for example, from degenerative disease, prosthetic discs are used to replace only the nucleus pulpous. Reference is made to my co-pending patent application Ser. No. 091,415,382, which discusses spinal anatomy, spinal physiology, disc degeneration, surgical and non-surgical treatments of disc disease, and the advantages of prosthetic disc replacement.
The annulus is formed of 10 to 60 fibrous bands which serve to control vertebral motion. One half of the bands tighten to check motion when the vertebra above or below the disc are turned in either direction. Restoring disc height returns tension to the annular noted in the prosthetic disc patent application. In addition, restoring annular tension decreases annular protrusion into the spinal canal or neural foramen. Thus, decreasing annular protrusion may eliminate pressure on the spinal cord or nerve roots.
At times the rotational, translational, and axial compression forces exceed the strength of the annular fibers. The excessive forces tear the annular fibers. A single event can tear one band to all the bands. Subsequent tears can connect to previous tears of a few bands resulting in a hole through the entire annulus fibrosis. Holes through the entire annulus fibrosis can result in extrusion of the nucleus pulpous. Extrusion of the nucleus pulpous is referred to as a xe2x80x9cherniated disc.xe2x80x9d Disc herniation can result in back pan, neck pain, arm pain, leg pain, nerve or spinal cord injury, or a combination of the above.
Since the annulus is innervated with pain fibers, acute annular tears without herniation of the nucleus can be painful. Unfortunately, the annular tears often do not heal completely. The chronic tears can result in neck pain, back pain, shoulder pain, buttock pain, or thigh pain. The chronic tears weaken the annulus fibrosis predisposing the disc to herniation or additional annular tears. My co-pending U.S. patent applications, Ser. No. 09/638,726, entitled xe2x80x9cMethods and Apparatus for Treating Disc Herniation,xe2x80x9d and 09/415,382, entitled xe2x80x9cArtificial Intervertebral Disc Replacementxe2x80x9d describe methods and apparatus for occluding annular defects.
Prosthetic replacement of the nucleus pulpous alone risks future problems arising from annular tears. Patients may continue to complain of pain from the stresses placed onto the weakened annulus. Secondly, tears of the annulus could result in extrusion of the prosthetic nucleus. In addition, remaining nucleus pulpous could herniate through annular tears.
Some prosthetic disc designs attempt to replace nucleus and annular functions. In general, these designs attach the prosthetic disc to the vertebrae. Many of the techniques in this area attach the prosthetic disc to the end plates of the vertebrae with screws, spikes, flanges, or porous surfaces for bone ingrowth. My co-pending U.S. patent application Ser. Nos. 09/322,516 and 09/415,382 describe methods and devices to assist the annulus in retaining remaining nucleus pulpous and a prosthetic nucleus. The entire contents of these applications are incorporated herein by reference.
The need remains, however, for a more extensive annulus augmentation technique. Failure at the disc vertebra interface could result in loosening of the prosthesis, however, and patients with loose prosthetic discs would likely require revision surgery.
This invention broadly resides in devices to augment the annulus fibrosis. More specifically, the present invention serves to aid the annulus in controlling vertebral motion, thereby preventing additional annular tears, and decreasing pain from annular tears. In contrast to previous designs, the devices would also assist a larger area of annulus, if not the entire annulus.
Devices according to the invention augment the annulus fibrosis and/or the annulus fibrosis attachment to the vertebrae above and below the disc. In the preferred embodiment, this is accomplished in at least two ways. First a biocompatible fabric or mesh such as Gore-Tex or Dacron is attached to the annulus. The material may be attached to the inside and/or outside of the annulus by stitches, staples, adhesives, or other suitable techniques. Alternatively, the fabric may be attached to the vertebra above and below the disc by screws, staples, tacks, or porous material for bone ingrowth such as titanium. Other methods of attachment to the annulus or vertebrae would also be acceptable if the overall goals of the invention are otherwise achieved.